I do this all the time on an android phone. On your computer, be sure you're signed into google using the same account as used on your android phone. Plan a route on google maps, then near the bottom of the directions click "Save to my maps". You can give it a name if you like. Over on your phone, open google maps and navigate to "my places", then click settings, then click "my maps." And you should see the map you created on your computer and saved earlier.